Temporal terms such as when, before, since, and while can convey information on the order, duration, and simultaneity of events. The order of acquisition of these terms is related to their use and to the concept each represents. In general, words of order, such as after and before, precede words of duration, such as since and until, used with the progressive verb tense (eating, running, jumping). These, in turn, precede terms of simultaneity, such as while. This hierarchy reflects a sequence of cognitive development.

Age (Months) Relationships Understood
24 Locational prepositions in and on
36 Locational preposition under
40 Locational preposition next to
48 (approx.) Locational prepositions behind, in back of, and in front of, difficulty with above, below, and at the bottom of; kinship terms mother, father, sister, and brother (last two are nonreciprocating)
60 Temporal terms before and after
60+ (school-age) Additional locational prepositions in temporal expressions, such as in a week; most major kinship terms by age 10; more precise locational directives reference the body (left and right)